const numberArr: number[] = [1, 2, 3];
const stringArr: string[] = ['apple', 'banana', 'coconut'];
const undefinedArr: undefined[] = [undefined, undefined, undefined];
const arr: (number | string | undefined)[] = [1, 2, 'apple', undefined];

type People = {
    name: string,
    age: number
}
interface PeopleInterface {
    name: string;
    age: number;
}
class PeopleClass {
    name: string;
    age: number
}

const peopleArr: People[] = [
    {name: '小红', age: 18},
    {name: '大红', age: 28},
]
